Former world champion Chris Algieri believes a welterweight unification between Errol Spence and Terence Crawford must happen this year.

Algieri was stopped by Spence (28-0, 22 KOs) in five rounds back in 2016.

Spence saw action in April, when he stopped Yordenis Ugas in ten rounds to unify the WBA, WBC, IBF welterweight titles.

Crawford (38-0, 29 KOs), who owns the WBO's title, retained his title in November with a stoppage win over Shawn Porter.

The two sides are currently negotiating the details of a potential showdown for the end of the year.

Last year, Crawford parted ways with longtime promoter Top Rank. His free agent status made the fight a more realistic possibility.

"That fight has to happen. It has to happen. The welterweight division is so deep. But as much as it's deep, you've got those two guys at the top. I think even number three is way below them. It's number one and number two, they have to fight," Algieri told Sky Sports.

"They're as close to their prime as they're going to get. They're only going to get away from it at this point. These guys fighting this year I believe has to happen to see the best fight possible."

Algieri is conflicted when trying to pick winner. He feels the match is so evenly matched that he could see either boxer pull it off.

"I always said Spence, but I think the more time that Terence spent at welterweight the more he grew into the weight class and what he's been able to do there with the guys that he's fought, it's edged into that stage where it really is a pick 'em fight," Algieri explained.

"Spence I believe is the bigger welterweight. He's more accustomed to that weight class. I do think he's probably fought the better competition there and both of them are riding high on big wins in their last fights.

"Between what Terence was able to do to Shawn Porter, which was absolutely incredible, Shawn's a fantastic fighter, and then what Spence was able to do to [Yordenis] Ugas, who is trouble for literally everybody, very, very impressive wins. So the two of them going into a fight with each other, post those wins, I mean it makes perfect sense and it's really hard to pick. I could tell you Spence today and Terence tomorrow."